In machines powered by internal combustion engines, fuel is supplied to the engine by a fuel transfer pump (FTP). The fuel for the engine, such as gasoline and diesel fuel, contains impurities that can cause build up of material in the fuel system components that ultimately requires maintenance to clean the components of the fuel system. Consequently, fuel is typically passed through a fuel filter before being communicated to the fuel transfer pump to remove the impurities and forestall the need for maintenance to the fuel system.
Because fuel in the tank or reservoir of the machine is not pressurized, low pressure at the inlet of the fuel transfer pump draws fuel from the reservoir through the fuel filter and into the fuel transfer pump for transmission to the engine. The fuel system works initially, but the filtered material builds up in the fuel filter and increases the pressure drop across the fuel filter necessary to draw fuel through filter. Eventually, the low pressure at the inlet of the fuel transfer pump is insufficient to draw fuel through the fuel filter and the engine cannot execute the combustion cycle. Fuel flow is improved in some know fuel systems by providing a clean fuel module (CFM) that filters the fuel while also providing a pressure boost to the fuel communicated the fuel transfer pump to improve the performance of the fuel transfer pump.
In one known configuration, a clean fuel module has a return manifold with a fuel inlet port connected to the fuel reservoir of the machine, a fuel outlet port connected to the fuel transfer pump, and a flow channel between the fuel inlet port and the fuel outlet port putting the inlet and outlet ports in fluid communication. The clean fuel module also includes a bypass or kidney loop where the fuel is filtered before transmission to the fuel transfer pump. To recirculate fuel through the bypass loop, the return manifold further includes a bypass outlet port proximate the fuel inlet port and a bypass inlet port proximate the fuel outlet port. The bypass outlet port is connected to an inlet of a CFM pump, an outlet of the CFM pump is connected to an inlet of a fuel filter, and an outlet of the fuel filter is connected to the bypass inlet port of the return manifold. The CFM pump increase the pressure of the fuel to force it through the fuel filter, and to provide the fuel to the inlet of the fuel transfer pump with a pressure boost that improves the performance of the fuel transfer pump.
Within the return manifold, a check valve is disposed within the flow channel to separate the fuel inlet port and the bypass outlet port from the fuel outlet port and the bypass inlet port. The check valve allows some flow of the pressurized fuel being communicated to the fuel transfer pump to the low pressure side of the check valve at the fuel inlet port, but the check valve closes to prevent fluid flow in the reverse direction from the fuel inlet port to the fuel outlet port. During normal operation, fuel bypasses the flow channel as the CFM pump discharges fuel from the fuel reservoir through the fuel filter and to the fuel transfer pump. The check valve creates a restriction between the fuel outlet port and the low pressure fuel inlet port to boost the pressure of the fluid transmitted to the fuel transfer pump while allowing some fuel flow through the check valve to prevent the outlet pressure from exceeding a maximum boost pressure. If the CFM pump stops working, the pressure at the fuel outlet port decreases and the check valve closes to prevent unfiltered fluid from flowing through the flow channel. At the same time, some bypass flow through the CFM pump and the fuel filter may be maintained as the low pressure at the fuel transfer pump continues to draw fuel.
The addition of the CFM pump increases the loading capacity of the fuel filter which, correspondingly, increases the pressure drop across the fuel filter. The fuel filters can be loaded with filtered material by the CFM pump to present a sufficiently high pressure drop across the fuel filter that the lower pressure created at the inlet of the fuel transfer pump is insufficient to draw fuel through the fuel filter on its own. With no flow through the fuel filter, and with the check valve closed, the engine is deprived of fuel, resulting in a “dead on haul road” condition where the engine stalls, thereby requiring the fuel filter to be serviced on location before moving the machine from the worksite.
In view of this, a need exists for an improved clean fuel module wherein a level of fuel flow is maintained during a CFM pump shutdown to maintain operation of the machine until the machine can be moved to an appropriate location for maintenance.